Method of drilling a hole in a rock

ABSTRACT

A method of controlling a rock drilling process by adjusting the percussion power and the feed force of a drilling machine. In the method, the drilling is carried out automatically in stages so that the percussion power and the feed force as well as drilling time or drilling depth are adjusted at a start-up drilling stage, and the ratio between the percussion power and the feed force is adjusted at a transition stage while increasing them until the set value of normal drilling is achieved. In normal drilling, the feed force is adjusted so that the rotation power remains at the set value.

This invention relates to a method of controlling a rock drillingprocess, wherein a percussion power and a feed force of a drillingmachine are adjusted to optimize the drilling process so that therotation power of the drill is no more than a preset limit value.

Rock drilling is usually based on a control system in which the drillercontrols the operation of the equipment on the basis of his practicalexperience. In such cases, the driller usually sets certain basic valueson the basis of the assumed conditions and does not have time to observepossible deviations and to control the operation accordingly. Especiallywith a drilling equipment comprising several booms, the driller is notable to observe all of them sufficiently efficiently and continuously tobe able to control them optimally. This usually results in partiallyinefficient drilling as well as equipment damages.

In systems based on automatic control of drilling, the feedback andcontrol are effected by using hydraulic actuating means in such a waythat one operating parameter, such as percussion, rotation or feed, iscontrolled on the basis of another parameter so that, for instance, Thefeed is retarded or the percussion is increased when the force requiredfor rotation increases. In these solutions, the adjustment is based onmere proportioning of certain operating parameters to each other withoutbeing able to more accurately set adjusting parameters dependent on theconditions.

U.S. Pat. No. 4,793,421 discloses a programmed automatic control systemaimed at optimizing the drilling. This system utilizes two groups ofparameters one of which is used to control the maximum rotation rate bysensing means and the other to control the supply of the maximum powerto the feed motor. In the US Patent, the maximum values of both rotationand feed are applied until the preset limit values are achieved ineither way or the drilling conditions require that the limit values bereset. The system of the US Patent is not directly applicable to rockdrilling as it adjusts only rotatory drilling. In addition, the systemmerely aims at maximizing the rotation power or feed power, while thedifferent drilling stages are not adjusted separately.

U.S. Pat. No. 4,354,233 discloses a solution iin which a computercompares a preset penetration value to an actual penetration value. Inthis method, the rotation rate and the axial load, i.e. feed, as well astorque and oscillation rate are adjusted. Changes in the adjustingvalues of the different drilling stages are not taken into account inany way.

U.S. Pat. No. 4,165,789 discloses a method in which the optimization isbased on the adjustment of the rotation of the drilling machine and theadjustment of the rotation resistance. The method aims at keeping oneparameter constant by adjusting the other parameter. The solution isvery simple and does not enable the optimization of the entire drillingprocess. Moreover, it does not in any way take into account thedifferent adjustments and parameter changes required at the differentdrilling stages.

U.S. Pat. No. 3,581,830 teaches measuring torque of the drill rod, thefeed force being used as an adjusting parameter. The feed force, thatis, the feed rate is decreased when the adjustment exceeds a presetvalue. This U.S. patent merely aims at keeping the torque strain of thedrill rod below a certain limit value and it does not in any way teachadjusting or not even aim at adjusting the drilling process by changingthe set values as required by the different drilling stages. A commondisadvantage of the systems of the above-mentioned patent documents isthat they adjust only a part of the drilling process and theirparameters are difficult if not impossible to change.

A further disadvantage of the prior art systems is that they typicallyresult in uneconomic drilling as the drilling parameters areinappropriate in one way or another. Systems based on hydraulic controlrespond rather slowly to sudden changes occurring during the drilling,as a result of which inefficient and uneconomic drilling as well asequipment damages occur very frequently. Furthermore, the fineadjustment and modification of systems based solely on hydraulics isdifficult and, in practice, it is impossible to make them monitor thedrilling conditions accurately and thus economically and technicallyefficiently.

The object of the present invention is to provide a method for effectingdrilling in such a way that the disadvantages of the known solutions areavoided and the drilling process is efficient and always takes intoaccount the drilling conditions. The method according to the inventionis characterized in that the drilling is controlled automatically instages by effecting the drilling stages sequentially one at a time, andthat the adjusting parameters affecting the percussion power and thefeed force are set at each drilling stage so that the percussion powerand the feed force are optimal for the drilling stage in question.

The basic idea of the invention is that the drilling is controlled atits different stages by parameters required by each particular drillingstage in such a way that each drilling stage is carried out as well andas efficiently as possible. An advantage of the invention is that thedrilling is as economic as possible while any unnecessary strains on thedrilling equipment are avoided and thus a considerable reduction inequipment damages is achieved as compared with the prior art techniques.

The invention will be described in greater detail in the attacheddrawings, in which

FIG. 1 shows schematically the principle of adjustment of the methodaccording to the invention;

FIG. 2 shows schematically the ratio between the drilling power and thefeed force when applying the method according to the invention:

FIG. 3 shows schematically the principle of adjustment of the contactbetween drill bit and rock: and

FIG. 4 shows schematically the operating range of the adjuster of FIG.3.

FIG. 1 shows schematically an adjusting diagram of the method accordingto the invention. An adjustment 1 comprises various operationalalternatives based on the prevailing conditions and situation. Itsprimary parts are sequential drilling adjustment 2, level adjustment 3of drilling parameters, and handling 4 of exceptional situations. Normalsequential drilling comprises four stages: start-up drilling 2a, a rampstage 2b through which the transition from start-up drilling to normaldrilling 2c takes place, and finally termination 2d of drilling. Inaddition, there is, in principle, a fifth stage, that is, a stop state,in which the equipment is ready to start the drilling. Handling ofexceptional situations comprises various possible exceptionalsituations, such as getting stuck 4a, broken drill bit 4b, rushing 4c,and insufficient penetration 4d, and their handling.

In the start-up drilling 2a, the percussion power and the feed ratelevel as well as the time or drilling depth during which the start-upparameters are applied are preset. Thereafter the transition fromstart-up drilling to normal drilling takes place through the ramp,whereby the control of the percussion and feed is increased towards theset power level through the rising ramp in such a way that the rise issubstantially linear. At this transition or ramp stage 2b, the parameterto be preset is the ratio between the percussion and the feed, that is,the ratio between the percussion power and the feed force. After theramp 2b, the normal drilling 2c is in progress, and the adjustment ofthe contact between bit and rock is added to the operation, and thelevel of feed is adjusted so that the rotation pressure of the rotationmotor of the drill rod remains at a preset value. The normal drillingfurther comprises an adjuster provided with a limiter. The adjusterensures that the feed is sufficient with respect to the set level ofdrilling power even when the rotation pressure is exceptionally high forone reason or another, e.g. when drilling obliquely for some reason orwhen the pressure oil is still cold at the onset of the drillingprocess. When the rotation pressure has increased sufficiently, theadjuster becomes passive, and a so-called fissure automation adjustmentis introduced for normal adjustment of the drilling process. The fissureautomation adjustment is known per se and can be realized in variousways, wherefore it is not described in greater detail herein. After Thecompletion of the hole, the return stage 2d follows, during which thedrill is usually retracted by a rapid movement, and when the drill bitis at a predetermined distance from its fully retracted position, themovement of the drill is retarded until it stops when the drill reachesits fully retracted position.

In the control of the drilling process, the above-mentioned fissuresituation, flushing and penetration, among other things, are monitored.

Fissure automation operates in response to the rotation pressure, whichis monitored, and when the rotation pressure exceeds a preset upperlimit, the drill is retracted immediately by a rapid movement, and thedrilling is then continued at reduced power a predetermined distanceafter the rotation pressure has decreased below a predetermined lowerlimit. Transition back to the preset level of drilling power through theramp stage 2b does not take place until after this predetermineddrilling at reduced power.

Flushing is supervised by monitoring the flow of flushing water at theflow rate. If the flushing is interrupted for some reason and is out ofoperation for a predetermined period of time, the drill is retractede.g. by simultaneous percussion until the flushing is again operative oruntil the drill reaches its retracted position. If the flushing startsto operate before the drill is in its retracted position, the drillingis again continued at reduced power a predetermined distance, whereafterthe transition from the reduced power To the set power level through theramp stage 2b takes place.

Penetration is supervised by setting a lower limit value for thepenetration rate, which prevents the drilling operation if the drilldoes not penetrate into the rock sufficiently rapidly during thedrilling. This may happen e.g. when the drill bit is broken or someother part of the equipment is damaged. In this case, the parameter tobe set is time. If the penetration rate during this preset time is lowerthan the preset penetration limit value, the supervision operation isstarted and thus the drilling operations are stopped. Correspondingly,the upper limit of the penetration rate is monitored so as to be able toprevent the drilling when the penetration rate is too high, that is, thedrilling equipment rushes onwards. The monitoring of such rushingprevents the percussion operation when the bit is out of contact withthe rock, thus preventing damage to the equipment, in this case, theparameter to be set is the time by which the penetration rate has toexceed the preset limit value to activate the supervision operation.

FIG. 2 shows schematically a block diagram for the adjustment ofdrilling. In the block diagram, the reference numeral 20 indicates theadjustment of the drilling power, in which a set value 21 for thedrilling power is set between 0 and 100%, and then a slope 22 is set bywhich the rising angle k0 of the drilling power is adjusted, i.e. thevelocity at which the value of the drilling power increases at the rampstage. The present actual value of the drilling power is further appliedto percussion power adjustment 30 in which an initial value 31 for thepercussion power, that is, the minimum value a1 of the percussion power,and correspondingly a slope 32 for the percussion power for adjustingits rising angle k1 are set. Adjusting means controlled by thisadjustment block are affected by an adjusting value P_(p) of thepercussion power. Correspondingly, the present actual value of thedrilling power affects an adjustment block 40, which sets a minimum feedforce for feed adjustment. Similarly as in the adjustment block 30, aminimum value 41 is set by which a minimum value a2 for the feed forceis adjusted, and correspondingly 42, by which the rise angle k2 of thefeed force is adjusted. From these values, a set value F_(m) isobtained, which indicates the minimum value of the feed force. This isapplied to an adjuster 50 for the feed force. Correspondingly, a setvalue 61 for the rotation pressure and an actual value 62 for therotation pressure are applied to an adjustment difference indicator 60so as to adjust the feed motor, the feed being adjusted in an adjustmentblock 70 on the basis of a difference 63 between these values. Theadjustment block 70 sets the upper and lower operating values for thepressure to keep the rotation pressure within a range appropriate forthe operation, which prevents the so-called saturation of the control ofthe feed in view of the operation. Within the defined range, the feed isadjusted by applying the obtained set feed value f_(s) to a comparator50, which selects the greater out of the values f_(min) and f_(s) andthen adjusts a feed level f_(c) by means of it. In the case of FIG. 2,the value of the drilling power also has a forward influence on thevalue of the feed, that is, the connection is of the feedforward type,in which the value of the feed changes in the same direction as thevalue of the drilling power, that is, the feedforward takes place fromthe power adjustment block 21 through the block 20 to the block 40 andfurther to the block 50 up to the adjusted feed value f_(c).Correspondingly, the measurement of the rotation pressure and thecontrol effected by means of it establish a feedback loop, in which thefeedback consists of the difference signal 63 generated by thedifference between the set value 61 and the actual measured value 62 ofthe rotation pressure. This signal adjusts the feed value f_(c) throughthe adjuster 70 in a reverse direction with respect to itself.

FIG. 3 shows schematically the principle of adjustment of the contactbetween bit and rock. The comparator 60 applies the difference 63between the set value 61 and the actual measured value 62 of therotation pressure to control the adjuster 70 for controlling the feed.The adjusted feed value is applied to an electro-hydraulic system 80from which the rotation pressure is measured by a measuring device 81and applied as the signal 62 to the difference indicator 60. Theelectro-hydraulic system 80, in turn, utilizes actuating means 90 fordrilling a hole in a rock 100. In this figure, the adjustment of thepercussion power and the drilling power as well as the adjustment of theminimum feed force have been omitted for the purpose of facilitating theunderstanding of the operating principle. In the arrangement shown inFIG. 3, the operation is based on giving the rotation pressure a certainset value and the pressure is attempted to be kept at this value bymeasuring the actual rotation pressure and by adjusting the feed bymeans of the pressure differences. The drill bit (not shown) is therebypressed against the surface to be drilled with a substantially constantforce, and it operates as efficiently as possible from the viewpoint ofdrilling technology. In this way, the frictions of the feeding mechanismand other factors affecting it and impairing the drilling result can becompensated for. If the feed is too weak, the drill tends to loosecontact with the rock, as a result of which the rotation pressure dropsand the pressure difference 63 increases. Consequently, the feed isincreased until the pressure difference is substantially 0.Correspondingly, if the value of the feed is too high, the rotationpressure increases and the pressure difference indicated by thecomparator 60 is negative, thus retarding the feed until the pressure issubstantially at its set value.

FIG. 4 shows schematically the operating range of the adjuster shown inFIG. 3. In the figure, the horizontal axis Pd represents the setdrilling power, and the minimum feed force a2 and the slope k2 rising inresponse to the drilling power are also presented in it. Below the linef_(min) defined by these, the prohibited area of the feed control isindicated by a cross-ruled area R, that is, the feed force always has tobe above the line f_(min) or at least equal to it. The curve f_(c)represents a specific adjustment curve which shows the adjustment of thefeed force as a function of the drilling power and other conditions.

The invention has been described above and shown in the drawingsschematically by way of example, and it is in no way restricted to thisexample.

I claim:
 1. A method of controlling a rock drilling process, wherein adrilling machine has percussion power (P_(p)) and feed force (f_(c))adjustable to optimize the drilling process so that the rotation powerof the drill is no more than a preset limit value, comprising the stepsof:controlling the drilling automatically in sequential stages;establishing at least three successive drilling stages including a firstdrilling stage for start-up drilling, a second stage comprising atransition stage from start-up drilling to a normal hole drilling stage,and a third stage comprising the normal hole drilling whereinappropriate values are set for drilling at each drilling stage to carryout the drilling; setting parameters affecting the percussion power(P_(p)) and the feed force (f_(c)) at each drilling stage so that thepercussion power (P_(p)) and the feed force (f_(c)) are optimal for eachdrilling stage.
 2. A method according to claim 1, including the steps ofusing the feed force (f_(c)) and preset drilling time or preset drillingdepth as parameters at the start-up drilling stage, setting thepercussion power (P_(p)) and the feed force for starting the drillingand starting drilling by drilling the hole for the preset time or overthe preset drilling depth.
 3. A method according to claim 2 includingthe steps of increasing the percussion power and the feed force in asubstantially evenly rising manner during the transition stage until theset values of the normal drilling are achieved, and, setting, during thetransition stage, the ratio between percussion power (P_(p)) and feedforce (f_(c)).
 4. A method according to claim 3 including the step ofadjusting the feed force (f_(c)) at the drilling stage so that rotationpower remains substantially equal to a preset value.